SYNTHESIS OF LIGANDS RELATED TO THE O-SPECIFIC ANTIGEN OF TYPE-1 SHIGELLA-DYSENTERIAE .3. GLYCOSYLATION OF 4,6-O-SUBSTITUTED DERIVATIVES OF METHYL 2-ACETAMIDO-2-DEOXY-ALPHA-D-GLUCOPYRANOSIDE WITH GLYCOSYL DONORS DERIVED FROM MONOSACCHARIDES AND OLIGOSACCHARIDES

Methyl O-(2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl)-(1 --> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranoside, obtained by silver trifluoromethanesulfonate-mediated condensation of methyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside and 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl bromide (3), was cleaved with dichloromethyl methyl ether (DCMME) to give O-(2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl)-(1 --> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl chloride (9). Condensations of 1,3,4,6-tetra-O-acetyl-alpha-D-galactopyranose with 3 and 9, followed by treatment of the products with DCMME yielded, respectively, glycosyl chlorides 12 and 17. Each of these, as well as 2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranosyl chloride was condensed with 4,6-O-substituted (benzylidene, tetraisopropyl-disiloxane-1,3-diyl, or benzyl) derivatives of methyl 2-acetamido-2-deoxy-alpha-D-glucopyranoside, using CH2Cl2, ether, or a mixture thereof as the solvent. The formation of the desired alpha-D-galactopyranosyl linkage was favored when ether was the solvent. Under these conditions, however, the combined yield of the condensation products decreased, especially when less reactive synthons were used. The alpha-linked products obtained were deprotected to give the methyl alpha-glycosides of the tetra, tri-, and the disaccharide related to the chemical repeating unit of the O-specific side chain of the lipopolysaccharide of Shigella dysenteriae type 1. Synthesis of methyl alpha-glycosides of three other constituents of the same polymeric antigen [alpha-L-Rha-(1 --> 3)-alpha-L-Rha, alpha-L-Rha-(1 --> 2)-alpha-D-Gal, and alpha-L-Rha-(1 --> 3)-alpha-L-Rha-(1 --> 2)-alpha-D-Gal] are also described.